Process for the production and purification of N-butyl acrylate

ABSTRACT

A process for the production of n-butyl acrylate (BuAcA) including the steps of esterifying acrylic acid (HAcA) with a n-butanol (n-BuOH) in a reaction zone, obtaining a condensate from the overhead vapors from the reaction zone which separates into organic and aqueous phases, feeding the organic phase comprising a major portion of BuAcA and minor portions of BuOH, water and light ends impurities to a finishing fractionation zone from which is obtained a side stream of a finished high purity BuAcA and an overhead condensate comprising BuAcA, BuOH, water, and light ends, recycling most of the overhead condensate from the finishing zone to the reaction zone, feeding the remainder of such condensate to a purge recovery zone together with a stream of makeup water, obtaining an overhead condensate from the purge recovery zone which separates into organic and aqueous phases each containing a portion of light ends produced in the reaction, recycling a portion of the organic phase as reflux to the purge recovery zone and discarding the remainder, and recycling at least a portion of the aqueous phase as feed to the purge recovery zone and discarding any remainder. Discarding of portions of the two phases of the overhead condensate has the effect of preventing or retarding the buildup of light ends in the system, while the amounts of water in the water makeup stream and the recycled portion of the aqueous phase of the overhead condensate to the purge recovery zone forms low-boiling azeotropes with components of the light ends thus facilitating separation of the light ends from the BuAcA and BuOH in the purged portion of the finishing zone overhead.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an improved process for the production andpurification of nbutyl acrylate.

2. Background Information and Description of Related Art

n-Butyl acrylate (BuAcA) is a commodity chemical useful for theproduction of acrylic resins and polymers and copolymers for paintformulations, solvent coatings, textile and leather finishes andadhesives and binders. One method of synthesizing BuAcA is to reactn-butanol (BuOH) with acrylic acid (HAcA) in the presence of an acidcatalyst, e.g., a sulfonic acid, in at least one reaction zone toproduce a mixture of BuAcA, water and several by-product impurities, andsubjecting the product mixture to purification in at least onedistillation zone, together with any of various schemes of reflux andrecycle streams among the reaction zone(s) and distillation zone(s) toobtain a BuAcA of relatively high purity. When any of these processesare operated, low boiling impurities produced in the reaction zone,i.e., those having boiling points near or below BuAcA, such as butylacetate and dibutyl ether and characterized as “light ends,” or “lights”must be systematically disposed of to prevent them from interfering withthe described reaction and compromising the purity of the BuAcA.However, this is often difficult to accomplish, e.g. by purging anappropriate stream, without also losing an unduly large amount of BuAcAproduct and unreacted BuOH, and/or incurring an unfavorably large costin energy consumption or purification equipment to prevent such loss.Thus, any improved process, which accomplishes an adequate disposal oflight ends while keeping the loss of BuAcA and unreacted BuOH and/or theincremental cost of energy and equipment to a minimum, is verydesirable.

U.S. Pat. No. 4,012,439, issued Mar. 15, 1977 to Erpenbach et al.,discloses a process for producing n-butyl acrylate by reacting acrylicacid with n-butanol in liquid phase and in contact with an acid cationexchanger as a catalyst. The process utilizes a single reaction zone andthree distillation zones.

U.S. Pat. No. 4,280,010, issued Jul. 21, 1981 to Erpenbach et al.,discloses a continuous process for making alkyl acrylates free fromether by reacting a C₁-C₄-alkanol in a molar ratio of 1:1 to 1:2 inliquid phase at 80° to 130° C. under 100-760 mmHg in the presence of acatalyst. The process employs a single reaction zone and twodistillation zones for separating the alkyl acrylate from unreactedalkanol and ether by-product.

U.S. Pat. No. 4,814,493, issued Mar. 21, 1989 to Dougherty et al.,teaches a process for the production of a n-butyl acrylate by reactionof n-butanol with acrylic acid in the presence of an esterificationcatalyst and soluble manganese or cerium. The system for carrying outthe process includes a reactor from which a butyl acrylate reactionproduct is sent to a finishing tower wherein the reaction product isseparated into a pure butyl acrylate stream, a volatile stream a portionof which is sent to a butanol recovery tower, and a residue stream whichis recycled to the reactor. A butanol stream from the butanol recoverytower is recycled to the reactor, and a residue stream from such toweris removed from the system.

South African Patent No. 9704628 issued Mar. 25, 1998, discloses aprocess wherein acrylic acid (HAcA) and n-butanol (BuOH) are reacted intwo reactors in series, and the product separated in two distillationcolumns to produce a stream comprising butyl acrylate (BuAcA), dibutylether (DBE), butyl acetate (BuAc), and BuOH. Such stream is furtherseparated in a splitter distillation column to provide an overheadfraction containing DBE, BuAc, and BuOH, and a bottoms fractioncontaining BuAcA and heavy end components (“heavies”), e.g., lowmolecular weight polymers of HAcA and/or BuAcA and Michael additionproducts. The overhead fraction from the splitter column is subjected tofurther distillation in the presence of water to separate BuOH and BuAcAfrom lights containing DBE and BuAc, with the BuOH and BuAcA beingrecycled to either or both reactors and the lights being sent to wastetreatment, while the bottoms fraction from the splitter distillation isrectified in a butyl acrylate distillation column to separate BuAcAproduct from heavies which are recycled to either or both reactors.

BRIEF SUMMARY OF THE INVENTION

In accordance with this invention, n-butyl acrylate (BuAcA) is producedby a process comprising reacting generally, amounts of n-butanol (BuOH)with acrylic acid (HAcA) in a reaction zone from which an overhead vapormixture is withdrawn comprising BuAcA, BuOH, water and light ends whichare organic by-product impurities having boiling points near or somewhatbelow that of BuAcA, and composed mainly of n-butyl acetate (BuAc) anddi-n-butyl ether (DBE). BuAcA, BuOH and water are removed in theoverhead vapor mixutre by a combination of binary and ternaryazeotropes. The vapor mixture is condensed to form a substantiallyorganic liquid phase comprising a major proportion of BuAcA and minorproportions of BuOH, water and light ends, and a substantially aqueousliquid phase comprising mainly water and a minor proportion of BuOH. Theorganic phase is fed to a finishing fractionation zone, from which aside stream of BuAcA product is withdrawn. Most of the overhead streamof the finishing fractionation zone composed of a portion of the totalof BuAcA and BuOH present and minor portions of water and light ends, isrecycled to the reaction zone. However, to prevent an undesirablebuildup of light ends in the system, a minor proportion of such overheadstream is purged and sent to a purge recovery fractionation zonetogether with a quantity of makeup water such that the formation of lowboiling azeotropes of water with components of the light ends isincreased thus facilitating separation of the light ends from thevaluable BuAcA and BuOH in the purge stream.

The overhead vapors from the purge recovery fractionation zone arecondensed to form separate organic and aqueous liquid phases, with eachphase containing a portion of the light ends produced in the system. Themajority of light end impurities remain in the organic phase compared tothe aqueous phase. A portion of the organic phase and optionally, aportion of the aqueous phase, are discarded such that the total amountof light ends in such discarded portions is comparable to the amount oflight ends produced in the reaction. By “discard” what is meant is toremove the stream or portion thereof from the process. The stream may befurther processed for proper disposal or further treated for recoveryand reuse. The remainder of the organic phase is recycled as reflux tothe purge recovery zone and at least a portion of the aqueous phase isrecycled as feed to the purge recovery zone.

The residue from the purge recovery zone, containing the bulk of theBuAcA and BuOH in the purged portion of the organic phase of thecondensed overhead from the finishing zone, and having a reduced lightends content is recycled to the reaction zone.

The process of the invention accomplishes the prevention of a buildup oflight ends in the system while minimizing the loss of BuAcA andunreacted BuOH, while keeping the cost of energy and new equipment toaccomplish this purpose, at a relatively low level.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a schematic representation of a preferred embodiment ofthe overall process of this invention.

DETAILED DESCRIPTION OF THE INVENTION

In the synthesis of n-butyl acrylate (BuAcA) in accordance with thisinvention, close to equimolar amounts of acrylic acid (HAcA) andn-butanol (BuOH) are fed to the reaction zone together with an acidesterification catalyst, e.g., about 1 to about 5 wt % based on theweight of total reaction mixture. Examples of the esterificationcatalyst include alkyl- or arylsulfonic acid such as methanesulfonic,benzenesulfonic or toluenesulfonic acid. Close to equimolar amounts ofHAcA and BuOH are fed to the reaction zone e.g. about 0.85 to about 1.3moles of BuOH per mole of HAcA. Stoichiometric excess of BuOH over HAcAis preferable to minimize the polymerizable free HAcA in the system,e.g. about 0.99 to about 1.3 moles of BuOH per mole of HAcA. To minimizepolymerization in the process, a polymerization inhibitor is preferablyalso fed and may be mixed with the HAcA. Those of skill in the art willappreciate the type and amount of inhibitor necessary to achievenon-polymerization, said type and amount being based on a variety offactors. The inhibitor may be, for example, phenothiazine or a phenoliccompound such as a dihydroxybenzene or a mono-lower alkyldihydroxybenzene, e.g. hydroquinone or its monomethyl or monoethylether.

In an embodiment of the invention, the esterification of HAcA with BuOHto produce BuAcA takes place primarily in the base reaction portion ofthe reaction vessel with the top portion of the vessel containingfractionation stages, e.g. in the form of trays and bubble caps orpacking, to separate the bulk of the BuAcA and unreacted BuOH fromresidue at the base of the column comprising primarily low molecularweight polymers of HAcA and BuAcA, catalyst and polymerizationinhibitor. Also remaining in the reactor are some quantities of freeHAcA and BuAcA. The reactor vessel operates at a temperature, e.g., inthe range of about 20 to about 150° C. and a pressure in the range ofabout 50 to about 400 mmHgA.

The overhead vapors from the reaction vessel consist mainly of BuAcA,lower amounts of BuOH and water and a minor amount of light ends, i.e.by-product organic compounds having somewhat lower boiling points thanBuAcA, such as n-butyl acetate (BuAc), n-butyl propionate (BuPr), DBE,secondary butyl acrylate (SBuAcA) and isobutyl acrylate (IBuAcA). Theoverhead vapors are condensed and separated into two phases, asubstantially organic phase having a major portion of BuAcA, reducedamounts of BuOH and water and the light ends, and a substantiallyaqueous phase comprising mainly water and BuOH. The organic phase issent to the finishing fractionization zone (the finishing tower) and theaqueous phase to a butanol recovery zone (the butanol recovery tower)wherein the BuOH is separated from the water for recycle to the reactionvessel.

The residue from the reaction vessel comprising mainly low molecularweight polymers of HAcA and BuAcA, some free HAcA, BuOH, catalyst andinhibitor is fed to a heat treater operating at a temperature, e.g., ofabout 150 to about 250° C. and a pressure, e.g., of about 80 to about150 psig, where some of the polymers are converted to the monomers. SeeHorlenko, U.S. Pat. No. 3,868,410 for further discussion regarding heavyend components. After a residence time of, e.g., about 1 to about 50min, most of the heat treated residue is recycled back to the reactionvessel, with a slip stream, e.g., of about 5 to about 20 wt % of theheat treated residue being removed to a heavy ends removal distillationunit, operating at a temperature of about 125 to about 200° C. and apressure of about 100 to about 700 mmHgA. The volatiles from the heavyends removal unit arc recycled to the reaction vessel while the residuefrom such unit is discarded.

The organic phase of the overhead condensate from the reaction vesselcomprises a major amount, e.g., about 80 to about 95 wt % of BuAcA, andminor amounts, e.g., about 5 to about 15 wt % of BuOH, about 1 to about3 wt % water, about 1 to about 10 wt % of light ends, and about 0.001 toabout 0.05 wt % of HAcA, is fed to the finishing tower, such toweroperating at a temperature, e.g., of about 20 to about 150° C. and apressure, e.g., of about 50 to about 400 mmHgA. Finished BuAcA having apurity of, e.g., about 99.0 to about 99.99 wt % is withdrawn as a vaporside stream from the finishing tower, and overhead vapors comprising,e.g., about 10 to about 80, preferably about 35 to about 70 wt % ofBuAcA, e.g., about 10 to about 80 wt %, preferably about 25 to about 70wt % of BuOH, and e.g., about 1 to about 10 wt % of light ends, arewithdrawn from the top of the finishing tower. The overhead vapors fromthe finishing tower are condensed and a portion of the condensate, e.g.,from greater than about 0 to about 75 wt %, preferably about 5 to about50 wt % is purged and sent to a purge recovery fractionation zone (thepurge recovery tower) with the remainder being recycled to the reactionvessel. Here, “greater than about 0” means at least a small quantitywhich is large enough or sufficient to operate the purge recovery tower.The residue from the finishing tower contains a major amount of BuAcAand is recycled to the reaction vessel.

The aqueous phase of the reaction vessel overhead condensate containing,e.g., about 1 to about 10 wt % of BuOH, and about 90 to about 99 wt % ofwater, is fed to the butanol recovery tower operating at a temperature,e.g., of about 70 to about 120° C. and a pressure, e.g., of about 1 toabout 5 psig. Alternatively the aqueous phase of the reaction vesseloverhead condensate may be discarded. The vapors from the top of thetower are primarily a binary azeotrope of BuOH and water which iscondensed into two immiscible phases, one being predominantly BuOH whichis recycled to the reaction vessel and the other a solution of a minoramount of BuOH in water which is recycled to the butanol recovery toweras reflux or discarded or recycled to the reaction vessel. The residuefrom the tower is composed primarily of water containing very littleBuOH and is discarded.

The purged portion of the finishing tower overhead condensate containsan amount of light ends which, when discarded, is sufficient to preventan undesirable buildup of light ends in the system. However, to minimizewastage of BuOH and HAcA utilized in the process, the purge stream isazeotropically distilled in the purge recovery tower to separate a majorportion of BuOH and BuAcA from the light ends. More specifically, thepurge recovery tower operates at a temperature, e.g., of about 30 toabout 150° C., preferably about 65 to about 110° C., a subatmosphericpressure of, e.g., about 50 to about 500 mmHgA, preferably about 200 toabout 350 mmHgA. The primary feed to the purge recovery tower is thepurged portion of the finishing tower overhead condensate, describedpreviously. Also entering the purge recovery tower is a portion of thesubstantially organic phase of the overhead condensate as reflux and inmany cases a portion of the aqueous phase of the overhead condensate asrecycle, both to be described in greater detail hereinafter; and amakeup supply of water. The water in the recycled aqueous phase of theoverhead condensate and the makeup water aid in the azeotropicdistillation of the light ends in the feed to separate them from theBuOH and BuAcA in such feed.

The overhead vapors from the purge recovery tower are condensed and thecondensate separated into organic and aqueous phases, with the organicphase being, e.g., about 70 to about 95 wt % of the total overheadstream and containing, e.g., about 20 to about 60 wt % of BuOH, about 10to about 60 wt % BuAcA, about 5 to about 20 wt % of light ends, andabout 5 to about 10 wt % of water. The aqueous phase from the condensedvapors make up the remainder of the total overhead containing, e.g.,about 85 to about 98 wt % of water, about 2 to about 15 wt % of BuOH,and generally less than about 1.0 wt % of light ends. As previouslymentioned, a portion of the condensate organic phase, e.g., about 10 toabout 80 wt %, is recycled to the purge recovery tower as reflux, theremainder being discarded, and at least a portion of the condensateaqueous phase, e.g. about 50 to about 100 wt %, is recycled to the purgerecovery tower as feed, with any remainder of this stream also beingdiscarded. The amount of water in the recycled aqueous phase iscorrelated with the amount of water in the makeup stream being fed tothe tower such that the total amount of water in the condensate aqueousphase and in the makeup stream is, e.g., from about 0 to about 50 wt %,preferably from about 1 to about 40 wt %, most preferably about 5 toabout 20 wt % of the organic feed going to the tower. It has beendetermined that this amount of water aids in the separation of lightends from the BuOH and BuAcA in the streams entering the tower byforming low boiling azeotropes with components of the light ends,particularly BuAc and DBE.

The purge recovery tower is operated such that the total amount of thelight ends in the discarded portions of the overhead condensate organicand aqueous phases is comparable to the amount of light ends produced inthe system so that there is no undesirable buildup of light ends in thesystem.

The residue composition from the purge recovery tower contains fromabout 10 to about 80 wt % of BuAcA and about 10 to about 80 wt % ofBuOH, as well as relatively smaller amounts of water and light ends, andis recycled to the reaction vessel.

The process of the invention may be further described with reference tothe drawing, which is a schematic diagram of a preferred embodiment ofthe inventive process. Into reaction vessel 1 are fed n-butanol (BuOH),acrylic acid (HAcA), and an acid esterification catalyst such asmethanesulfonic acid (MSA) tirough lines 2, 4, and 5 respectively. Apolymerization inhibitor is also typically employed throughout theprocess, and added at appropriate locations and appropriateconcentrations. Those of skill in the art will recognize appropriatelocations and concentrations to utilize. Conditions of temperature andpressure are maintained in reaction vessel 1 to cause a reaction of HAcAand BuOH present in some excess to form n-butyl acrylate (BuAcA) andwater, and small amounts of various by-products such as light endsincluding n-butyl acetate (BuAc) and di-n-butyl ether (DBE) and heavyends such as low molecular weight polymers of HAcA and BuAcA. Vapors ofthe more volatile compounds present including BuOH, BuAcA, water andlight ends rise into the fractionization zone situated immediately abovethe reaction zone of reaction vessel 1. These vapors are forwardedthrough line 6 into condenser 8 from which the liquid condensate flowsthrough 9 into separator 10 where the condensate is separated intoimmiscible substantially organic phase 11 and aqueous phase 12. Theorganic phase condensate containing predominately BuAcA is fed throughline 14 to finishing tower 15 from which high purity finished BuAcA iswithdrawn as a sidestream through line 18. The overhead vapors fromtower 15 containing significant amount of BuOH and BuAcA and lesseramounts of water and light ends, are fed through line 19 to condenser20, and the residue from tower 15 containing primarily BuAcA is recycledthrough line 21 to reaction vessel 1. The diagram indicates stream 21forwarded to the base of vessel 1. Those of skill in the art willappreciate that this stream may be forwarded to any location in 1 asappropriate. Most of the condensate from condenser 20 is recycledthrough line 22 to reaction vessel 1. However, a minor portion of thecondensate is purged and fed through line 24, to purge recovery tower 25together with a supply of makeup water through line 26. The addition ofmakeup water acts to keep the content of water in purge recovery towersufficient to form water azeotropes with various of the light ends andrender more efficient the separation of the light ends in purge recoverytower 25. The overhead vapors from purge recovery tower 25 containingsignificant amounts of BuOH, water, light ends, and BuAcA are fedthrough line 28 to condenser 29. The residue of tower 25 containingsignificant amounts of BuAcA and BuOH is stripped of light ends and isrecycled through line 30 to reaction vessel 1. The condensate fromcondenser 29 is fed through line 31 to separator 32 where it separatesinto organic and aqueous phases. A part of the organic phase is recycledthrough line 34 to purge recovery tower 25 as reflux while the remainderis withdrawn through line 35 and discarded. Similarly, a part of theaqueous phase is recycled through line 36 to purge recovery tower 25 andthe remainder withdrawn through line 38 and discarded. The foregoingdiscarding of portions of the organic and aqueous phases from separator32 act to keep the light ends of the overall system in balance.

The residue from reaction vessel 1 comprising mainly low molecularweight polymers of HAcA and/or BuAcA and Michael addition products isfed through line 39 to heat treater 40 where part of the heavies areconverted to HAcA and/or BuAcA. Most of the heat-treated stream fromheat treater 40 containing increased amounts of HAcA and/or BuAcA isrecycled through line 41 to reaction vessel 1. However, to prevent abuild up of heavy ends in the system, a slip stream from the heattreater 40 is fed through line 42 to a heavy ends removal unit 44. Thevapors from unit 44 containing a significant amount of HAcA and/or BuAcAare condensed and recycled through line 45 to reaction vessel 1 whilethe residue from unit 44 are withdrawn through line 46 and discarded.

Aqueous phase 12 from separator 10 containing some BuOH is fed throughline 48 to an intermediate point of butanol recovery tower 49.Optionally, stream 48 may be discarded. The overhead vapors from 49comprising an azcotrope of BuOH with water is fed through line 50 tocondenser receiver 51 where it separates into an organic phasecomprising an increased amount of BuOH which is recycled to reactionvessel 1 through line 52, and an aqueous phase comprising some amount ofBuOH which is either fed as reflux to butanol recovery tower 49 throughline 54 or alternatively, is discarded or recycled to the reactionvessel. The residue containing predominantly water is withdrawn throughline 55 and discarded.

What is claimed is:
 1. A process for producing n-butyl acrylate (BuAcA)comprising: (a) esterifying acrylic acid (HAcA) with n-butanol (BuOH) ina reaction zone from which an overhead vapor mixture is withdrawn, saidvapor mixture containing BuAcA, BuOH, water and light ends components,said light ends components having boiling points near or somewhat lowerthan that of BuAcA, (b) condensing said vapor mixture to form an organicphase containing BuAcA, BuOH, light ends, and an aqueous phasecontaining predominantly water and BuOH, (c) feeding said organic phaseto a finishing fractionation zone, (d) withdrawing BuAcA having a highdegree of purity from said finishing zone, (e) withdrawing andcondensing the overhead vapors from said finishing zone comprising amajor portion of the total of BuAcA and BuOH present and minor portionsof water and light ends, (f) recycling a major portion of said overheadcondensate of the finishing zone to the reaction zone, (g) feeding aminor portion of said overhead condensate of the finishing zone togetherwith a stream of makeup water, to a purge recovery fractionation zone,(h) condensing the overhead vapors of said purge recovery zonecomprising significant amounts of BuOH, BuAcA, water and light ends toform an organic phase containing BuOH, BuAcA, and lights ends and anaqueous phase containing some BuOH, BuAcA and light ends, (i) recyclinga portion of said organic phase of the overhead condensate from thepurge recovery zone back to said purge recovery zone as reflux, (j)discarding the remainder of said organic phase, (k) recycling at least aportion of said aqueous phase of the overhead condensate of the purgerecovery zone as feed to the purge recovery zone, with any remainderbeing discarded, wherein, the total amount of water in said recycledportion of the aqueous phase of the overhead condensate of the purgerecovery zone and said makeup stream of water having the effect ofincreasing the formation of low boiling azeotropes with the componentsof light ends entering the purge recovery zone.
 2. The process of claim1 wherein said overhead condensate from the finishing zone comprisesabout 10 to about 80 wt % of BuAcA, about 10 to about 80 wt % of BuOHand about 1 to about 10 wt % of light ends.
 3. The process of claim 2wherein said range of BuAcA is about about 35 to about 70 wt % and saidrange of BuOH is about 25 to about 70 wt %.
 4. The process of claim 1wherein from greater than about 0 to about 75 wt % of said overheadcondensate from the finishing zone is fed to said purge recovery zonewith the remainder of said condensate being recycled to the reactionzone.
 5. The process of claim 4 wherein the amount of said overheadcondensate from the finishing zone fed to the purge recovery zone isabout 5 to about 50 wt %.
 6. The process of claim 1 wherein said purgerecovery zone operates at a temperature in the range of about 30 toabout 150° C., and a pressure in the range of about 50 to about 500mmHgA.
 7. The process of claim 6 wherein said range of temperatures inthe purge recovery zone is about 65 to about 110° C. and said range ofpressures in said zone is about 200 to about 350 mmHgA.
 8. The processof claim 1 wherein said organic phase of the overhead condensate of thepurge recovery zone is about 70 to about 95 wt % of the total condensateand contains about 20 to about 60 wt % of BuOH, about 10 to about 60 wt% BuAcA and about 5 to about 20 wt % light ends, with about 10 to about80 wt % of said organic phase being recycled to said purge recovery zoneas reflux and the remainder being discarded.
 9. The process of claim 8wherein said aqueous phase of the overhead condensate of the purgerecovery zone contains about 2 to about 15 wt % of BuOH, and less thanabout 1.0 wt % of light ends with about 50 to about 100 wt % of saidaqueous phase being recycled as feed to said purge recovery zone and theremainder being discarded, the amount of light ends in the discardedportions of said organic and aqueous phases of the overhead condensateof the purge recovery zone being such as to prevent or retard thebuildup of light ends in the system.
 10. The process of claim 1 whereinthe total of the water in the makeup stream of water to the purgerecovery zone and the recycled portion of the aqueous phase of theoverhead condensate of the purge recovery zone are correlated such thatthe total amount of water in the two streams is in the range of fromabout 0 to about 50 wt % of all the streams being fed to the purgerecovery zone.
 11. The process of claim 10 wherein said range of wateris about 5 to about 20 wt %.
 12. The process of claim 1 wherein theresidue from said purge recovery zone comprising a major amount of thetotal of BuAcA and BuOH present and largely stripped of light ends isrecycled to said reaction zone.